The young man came to the emergency room at Tampa General Hospital. For almost an hour, he'd been having trouble speaking, and the right side of his face and right arm were weak. He was having a stroke.

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But why? He was 26, healthy but for asthma, didn't smoke tobacco, didn't drink, had no family history of blood clots, heart disease or stroke. Doctors treated him, and when his condition improved, they asked what he was doing before the stroke.

Smoking "spice," he said.

It was the street name for synthetic marijuana, plant clippings hosed with chemicals and rolled into a joint. Doctors tucked away the information as noteworthy.

But although Tampa is big, the Comprehensive Stroke Center at TGH is a smaller world. When a 19-year-old woman came in later with similar symptoms, the stroke team recognized her. She'd been there to see her brother during his stroke.

"That's the only reason it even dawned on us to ask, 'Hey, were you by any chance smoking spice?' " said W. Scott Burgin, neurology professor at the University of South Florida and director of TGH's stroke center.

Indeed, she had smoked it. And like her brother, she had smoked from the same batch right before the symptoms started.

The cases prompted a study by a USF neurology team to determine if there may be a link between synthetic marijuana and strokes in healthy, young adults. The results appeared in a November article published in the American Academy of Neurology's journal, Neurology, and are generating discussion in the field.

More research has to be done, said Burgin, the paper's senior author. There's always a chance the siblings shared a medical predisposition to strokes, although doctors didn't find one. But since submitting the paper, he said, he has seen at least two probable spice-stroke cases at the hospital, in people who were not related to each other.

The sibling strokes showed the pattern of a clot traveling from the heart to the brain. That made sense to Burgin, who said many complaints people have after smoking spice are cardiac, like heart palpitations and chest pain.

Spice, also called K2, has been sold for years in stores under the guise of "herbal incense" or "potpourri." The packets are labeled "not for human consumption," which helped the product skirt regulation. Before 2010, it was not controlled in any way.

President Barack Obama signed a bill in 2012 banning several types of synthetic drugs. And 43 states have bans on spice, including Florida, where Attorney General Pam Bondi has taken up the cause. Local law enforcement agencies have done high-profile mini-mart sweeps, confiscating loads of neon packets with trippy pictures of Dopey from Snow White and the Seven Dwarves, and names like Kush Max, Impact and Mind Warp.

But people still buy spice on the Internet, or at mom-and-pop convenience stores. And manufacturers keep working to make chemical combinations that aren't yet banned. A 2012 survey from the University of Michigan found one in nine American high school seniors reported using spice, making it their second-most-used illegal drug after natural marijuana.

Spice is not natural marijuana. It's far more potent, experts say, and can make people crazed.

"I don't think the two things should be confused with one another," Burgin said. "This is a clandestine, artificial designer drug that we're talking about here, made in a lab."

St. Petersburg police officer Patrick McGovern deals with spice arrests every day. Most people he sees with spice are between 20 and 30, he said. He can tell right away when someone has been smoking it because they're either very lethargic or completely aggressive, acting wild, resisting arrest.

"I've never seen anything like this and I've been doing this 21 years," he said. "I know when someone's been smoking marijuana, the real stuff. It's mellow, giggly. Typical. This stuff is weird."

A mentally-ill man was said to have smoked spice before he stole an ax and chased people down a St. Petersburg street in October. Last year, medical examiners listed synthetic marijuana as a factor in the death of a 19-year-old man who drowned in 14 inches of water in a Clearwater creek.

While more medical research on spice will come, Burgin said the USF case studies offer immediate takeaways.

One is for doctors. They need to ask about drugs like spice, MDMA (usually called "molly") and bath salts, he said, things that don't always show up on traditional drug screens, things patients don't like to admit without prodding.

"We are all taught to ask about marijuana and cocaine and amphetamines and alcohol and tobacco," he said. "We didn't have synthetic marijuana and molly and some of these other drugs when I went to medical school."

The other takeaway is for the general public, for anyone who would consider putting untested chemicals in his body.

"Would you just walk down the street and pick up a pill bottle off the ground that had no label on it and take those?" Burgin said. "That's probably safer in some ways than this."

Stephanie Hayes can be reached at shayes@tampabay.com or (813) 226-3394.